1. Field of the Invention
The invention relates generally to a method of manufacturing a capacitor in a semiconductor device, and more particularly to, a method of manufacturing a capacitor in a semiconductor device which can prevent oxidization of the surface of an underlying electrode to improve the characteristic of the leak current of a Ta.sub.2 O.sub.5 capacitor, upon a thermal treatment process performed after Ta.sub.2 O.sub.5 is deposited in order to form a dielectric film, in a Ta.sub.2 O.sub.5 capacitor of a MIM (Metal Insulator Metal) structure using tungsten (W) as an underlying electrode.
2. Description of the Prior Art
Generally, when manufacturing a Ta.sub.2 O.sub.5 capacitor in a memory device, if metal materials such as Tungsten are used as underlying electrode materials, the work function of the metal materials with poly-silicon is large. Thus, the thickness of the effective oxide film Tox can be reduced and thus the leak current in the thickness of the same effective oxide film can also be reduced. Further, the value of .DELTA. C depending on the bias voltage is small. As a Ta.sub.2 O.sub.5 dielectric film lacks oxygen in the film formed by Ta.sub.2 O.sub.5 deposition process and also contains impurities such as carbon or hydrogen etc., in order to secure the dielectric characteristic of the Ta.sub.2 O.sub.5 capacitor, oxygen must be flowed into it and a subsequent process for removing impurities must be performed after the Ta.sub.2 O.sub.5 deposition is completed.
This subsequent process is mainly thermally performed under oxygen atmosphere at a higher temperature, thus securing the dielectric characteristic of a Ta.sub.2 O.sub.5 dielectric film. However, if the temperature of the thermal process is too high or the time of the thermal treatment is too long, upon thermal treatment process, the surface of the underlying tungsten electrode is oxidized to form a WO.sub.3 film. The WO.sub.3 film has the dielectric constant of about 42, which is higher than that of Ta.sub.2 O.sub.5 dielectric film having about 25. However, when creating the WO.sub.3 film, there is a possibility that oxygen within the Ta.sub.2 O.sub.5 dielectric film can be diffused into the underlying tungsten electrode. Also, due to the difference of the thermal expansion coefficient with the Ta.sub.2 O.sub.5 dielectric film, there is a problem that the characteristic of the leak current of the Ta.sub.2 O.sub.5 capacitor becomes degraded since a phenomenon of film lifting of the film is generated.